Electrochemical Behavior of L-Tyrosine at Poly (Dicyclomine Hydrochloride) Film Modified Carbon Paste Electrode: A Cyclic Voltammetric Study

ISSN 2350-1030
International Journal of Recent Research in Physics and Chemical Sciences (IJRRPCS)
Vol. 3, Issue 1, pp: (7-16), Month: April 2016 – September 2016, Available at: www.paperpublications.org
Page | 7
Paper Publications
Electrochemical Behavior of L-Tyrosine at Poly
(Dicyclomine Hydrochloride) Film Modified
Carbon Paste Electrode: A Cyclic
Voltammetric Study
Deepak M.P1
, Mamatha G.P2
1
Department of Chemistry, Kuvempu University, Jnana Sahyadri, Shankaraghatta, Shimoga, Karnataka, India.-577 451
2
Department of Pharmaceutical Chemistry, Kuvempu University, Post Graduate Centre, Kadur, Chickmagalore, Dt.
Karnataka, India.-577 548
Abstract: An electrochemical method for the determination of L-Tyrosine (LTY) using a dicyclomine
hydrochloride (DICY) polymer film modified carbon paste electrode. The surface morphology of poly (DICY)
modified carbon paste electrode was characterized by SEM. The modified electrode showed excellent electro
catalytic activity towards the oxidation of LTY in 0.1 M phosphate buffer solution of pH 6.5. The effect of pH,
concentration and scan rate were studied at the bare carbon paste electrode and poly (DICY) modified carbon
paste electrode were investigated. Increase of LTY concentration shows linear increase in oxidation peak current.
The linear relationship was obtained between the anodic peak current (Ipa) and concentration LTY in range 2×10-5
M to 1×10-3
M with correlation coefficient of 0.9984. The low detection limit (LOD) and low quantification limit
(LOQ) of LTY were detected. The cyclic voltammetric studies indicated that the oxidation of LTY at the modified
electrode surface was irreversible; adsorption controlled and undergoes a one electron transfer process at the poly
(DICY) film modified carbon paste electrode. The modified electrode showed high sensitivity, detection limit, high
reproducibility, easy preparation and regeneration of the electrode surface.
Keywords: Carbon Paste Electrode, Cyclic Voltammetry (CV), Dicyclomine Hydrochloride (DICY), Irreversible,
L-Tyrosine (LTY), Scanning electron microscope (SEM).
1. INTRODUCTION
L-Tyrosine (LTY) or 4-hydroxyphenylalanine is one of the 22 amino acids that are used by cells to synthesize proteins.
The word "tyrosine" is from the Greek tyri, meaning cheese, as it was first discovered in 1846 by German chemist Justus
von Liebig in the protein casein from cheese [1, 2]. It is called tyrosyl when referred to as a functional group or side
chain. Aside from being a proteogenic amino acid, tyrosine has a special role by virtue of the phenol functionality. It
occurs in proteins that are part of signal transduction processes. It functions as a receiver of phosphate groups that are
transferred by way of protein kinases (so-called receptor tyrosine kinases). Phosphorylation of the hydroxyl group
changes the activity of the target protein. A tyrosine residue also plays an important role in photosynthesis. In chloroplasts
(photosystem II), it acts as an electron donor in the reduction of oxidized chlorophyll. In this process, it undergoes
deprotonation of its phenolic OH-group. This radical is subsequently reduced in the photosystem II by the four core
manganese clusters.

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There are number of electrochemical methods reported for the determination of tyrosine using various modified electrodes
which include, L-serine polymer film [3], multiwall carbon nanotube [4], poly (9-aminoacridine) [5] and gold
nanoparticles [6] modified with glassy carbon electrode, FTIR spectroscopic studies at poly crystalline platinum surface
[7] and polyamide modified carbon paste electrode along with tryptophan [8] and iron(III) doped zeolite modified with
carbon paste electrode along with dopamine [9] amperometry and cyclic voltammetry at carbon fiber microelectrodes
applied to single cell analysis along with tryptophan [10]. Numerous methods have been reported for tyrosine
determination mainly spectrophotometric, fluorimetric, flow injection, chemiluminescence, liquid chromatography-
tandem mass spectrometry, gas chromatography-mass spectrometry and high-performance liquid chromatography [11-
17].
Limited work has been done in the area of carbon paste electrode for the determination of L-Tyrosine. Therefore in the
present work we used dicyclomine Hydrochloride polymer modified CPE to study the electrochemical behavior of L-
Tyrosine and polymerization of dicyclomine hydrochloride has been established for the determination of L-Tyrosine for
the first time. This electrode showed excellent electrocatalytic activity towards the oxidation of L-Tyrosine, the
determination and sensitivity is significantly improved compared to bare CPE.
2. EXPERIMENTAL SECTION
2.1 Reagents:
Dicyclomine Hydrochloride (DICY) and L-Tyrosine (LTY) were purchased from Sigma Aldrich and all other chemicals
were of analytical grade. The electropolymerisation of dicyclomine hydrochloride was performed in 0.1 M phosphate
buffer solution. The phosphate buffer solution was prepared from KH2PO4 and K2HPO4, the pH was adjusted with H3PO4
and 0.1 N NaOH solutions. The stock solution of L-Tyrosine (10 mM) was prepared by dissolving in 0.1 N NaOH. Other
chemicals used were of analytical grade except for spectroscopically pure graphite powder. All solutions were prepared
with doubly distilled water. Freshly prepared LTY solution is used prior to measurements.
2.2 Apparatus:
Electrochemical measurements were carried out with Electroanalyser model EA-201 chemlink system in a conventional
three-electrode system. The working electrode was carbon paste electrode, having cavity of 3 mm diameter. The counter
electrode was platinum electrode with a saturated calomel electrode (SCE) as a standard reference electrode for
completing the circuit.
2.3 Modification Procedure:
2.3a. Preparation of bare carbon paste electrode:
The Bare Carbon paste electrode was prepared by hand mixing of 70% graphite powder and 30% silicon oil to produce a
homogenous carbon paste which was then packed into the cavity of a homemade carbon paste electrode and smoothed on
a weighing paper.
2.3b. Preparation of the Dicyclomine hydrochloride polymer film modified carbon paste electrode:
The polymer film modified electrode was prepared by electrochemical polymerization of DICY in 0.1 M phosphate buffer
solution of pH 6.5 containing 1 mM DICY with cyclic voltammetric in the potential range 100 to 1400 mV at the scan
rate of 100 mVs-1
. After 10 cycles, the surface of the electrode was washed with double distilled water to remove the
physically adsorbed material, air dried and used for the electrochemical studies.
3. RESULT AND DISCUSSION
3.1 Electropolymerisation of Dicyclomine Hydrochloride (DICY) on Carbon Paste Electrode:
Electropolymerzation of dicyclomine hydrochloride (DICY) was performed on bare carbon paste electrode (BCPE). The
cyclic voltammograms for the electropolymerisation of 1mM of DICY in 0.1 M phosphate buffer solution on CPE is
shown in Fig.1, which displays the continuous cyclic voltammetric of 1mM DICY monomer by scanning in the potential
range of 100 to 1400 mV for 10 cycles. During the electropolymerisation process, indiscernible peaks started to appear

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after 5th
cycle. An anodic peak at 861 mV potential was observed due to the formation of poly (DICY). The peak
descended gradually with the increase in cyclic time; such decrease indicates the poly (DICY) membrane forming and
depositing on the surface of the CPE by electropolymerisation. After polymerization the poly (DICY) modified carbon
paste electrode was carefully rinsed with distilled water to remove the physically adsorbed material. Then the film
electrode was transferred to an electrochemical cell and cyclic voltammetric sweeps were carried out to obtain
electrochemical steady state.
The thickness of poly (DICY) film could be controlled by the cyclic number of voltammetric scans during the
electrochemical modification. The effect of the thickness of poly (DICY) film on the electrochemical response was
investigated by cyclic voltammetric technique. The current (Ipa) response of poly (DICY) films increase gradually as the
number of cycles increases during film formation from 5 to 10 cycles. Afterwards Ipa starts to decrease by increasing the
number of cycles which was examined up to 30 cycles (Fig. 1a).In order to obtain better oxidation peak and higher
sensitivity of current for the electrochemical response of DICY, 10 scans were chosen to control the thickness of the poly
(DICY) film.
200 400 600 800 1000 1200 1400
286.1 
Current()
Voltage (mV)
Fig.1: Cyclic voltammograms for the electro polymerization of 1 mM of DICY in 0.1 M phosphate buffer solution on carbon
paste electrode.
5 10 15 20 25
120
140
160
180
200
220
240
260
280
300
Ipa
()
Number of cycles
Fig.1a. Plot of anodic peak current vs. number of cycles of Dicyclomine hydrochloride.
3.2 SEM Characterization of poly (Dicyclomine Hydrochloride) modified carbon paste electrode:
Fig. 2 (a&b), explain the surface morphology of bare carbon paste electrode (BCPE) and poly (DICY) modified carbon
paste electrode respectively using scanning electron microscope (SEM). The surface of bare CPE was formed by
irregularly shaped micrometer-sized flakes of graphite. Whereas the modified electrode had atypical uniform arrangement
of DICY molecules on the surface of CPE [18].

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Fig.2: SEM images of bare carbon paste electrode (a) and poly (DICY) modified carbon paste electrode (b).
3.3 Electrochemical response of potassium ferrocyanide at poly (DICY) modified carbon paste electrode:
Fig. 3 shows the electrochemical response of 1 mM potassium ferrocyanide in 1M KCl at bare carbon paste electrode
(BCPE) curve „b‟ and at poly (DICY) modified carbon paste electrode curve „a‟. Anodic peak potential Epa 290 mV with
peak current Ipa of 13.38 µA and cathodic peak Epc 50 mV with peak current Ipc of 8.23 µA respectively. After
modification with poly (DICY) modified carbon paste electrode which shows enhancement of both electrochemical
anodic peak potential (Epa) 234 mV with peak current (Ipa) of 23.9 µA and cathodic peak potential (Epc) 163 mV with peak
current (Ipc) of 14.55 µA respectively were observed. The surface area of bare carbon paste electrode is 0.0258 cm2
.
Whereas, effective surface area of the modified electrode was found to be 0.0365 cm2
.
-200 0 200 400 600
26.9  (b)
(a)
Current()
Voltage (mV)
(b)At BCPE
(a)At MCPE
Fig. 3. Comparison of 1 mM K4[Fe(CN)6] in 1 M KCl solution at poly (DICY) modified carbon paste electrode(a)and bare
carbon paste electrode (b).
3.4 Electrochemical behavior of L-Tyrosine at poly (Dicyclomine Hydrochloride) modified carbon paste electrode:
Fig. 4 shows cyclic voltammograms of 0.1 mM L-Tyrosine in 0.1 M phosphate buffer solution of pH 6.5 at bare carbon
paste electrode (curve „b‟) and at poly (DICY) modified carbon paste electrode (curve „a‟).The curve „c‟represents cyclic
voltammogram of the blank solution at poly (DICY) modified carbon paste electrode. Above studies showed that only one
oxidation peak at 1009 mV potential with peak current of 12.49 µA at bare CPE, whereas an oxidation peak at 991mV
potential with peak current of 28.70 µA at the poly (DICY) modified carbon paste electrode respectively in the potential
range 100 to 1300 mV. No reduction peak was observed in the reverse scan, suggesting that the electrochemical reaction
is a totally irreversible process and the oxidation peak current at the bare CPE is broad due to slow electron transfer, while
the response was considerably improved at the poly (DICY) modified carbon paste electrode and the peak potentials
shifted to negative direction, the shape of the peak turns sharper and the peak current increased significantly.

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200 400 600 800 1000 1200
28.7
c
b
a
Voltage (mV)
Current()
Fig.4: Comparision of 1 mM LTY at poly (DICY) modified carbon paste electrode (a), bare carbon paste electrode (b) and
blank solution in phosphate buffer at poly (DICY) modified carbon paste electrode (c); pH 6.5, scan rate 50 mVs-1
.
3.5 Effect of pH:
The pH influence was investigated by cyclic voltammetric measurement at different pH values between 3.5 and 9.0 as
shown in Fig. 5a. The maximum response of current was observed at pH 6.5. In order to obtain the maximum bioactivity
and optimal sensitivity, phosphate buffer solution of pH 6.5 and scan rate 50 mVs-1
were selected for our experiments.
The oxidation peak current increases with increase of pH from 4.5 to 6.5 and becomes maximum and peak potential
shifted negatively. While pH beyond 6.5, a great decrease of the oxidation peak current could be observed, then it
decreased gradually with the further increase in pH of the solution as shown in Fig. 5a and the oxidation peak potential
decrease with increase of pH as shown in Fig. 5b. A linear relationship was obtained between the anodic peak potential
and pH of the solution in the range 3.5 – 9. The corresponding linear regression equation is
Epa (mV) = 1086 – 28.89pH (R = 0.99149)……………………….. (1)
With a negative slope of 28.89 indicating that the number of electrons and protons are equal in the electrochemical
oxidation of LTY at poly (DICY) modified carbon paste electrode.
3 4 5 6 7 8 9
12
14
16
18
20
22
24
26
28
30
Ipa
()
pH
Fig.5a: Plot of anodic peak current vs. pH (3.5 – 9.0) of 0.1 mM LTY at Poly (DICY) modified carbon paste electrode.

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3 4 5 6 7 8 9
820
840
860
880
900
920
940
960
980Epa
(mV)
pH
Fig.5b: Plot of anodic peak potential vs. pH (3.5 – 9.0) of 0.1 mM LTY at poly (DICY) modified carbon paste electrode.
3.6 Effect of scan rate:
The effect of scan rates on the electrochemical response of 0.1 mM LTY at poly (DICY) modified carbon paste electrode
was studied at different scan rates. Redox peak current increase linearly with the scan rate in the range10, 20, 30, 40, 50,
60, 70, 80, 90 and 100 mVs-1
.The cyclic voltammograms were shown in Fig. 6a. However linearity obtained for the plot
of the anodic peak current vs. scan rate with a correlation coefficient of 0.9943 shown in Fig. 6b.The linear relationship
with a correlation coefficient of 0.9988 obtained between the peak current and square root of scan rate in the range of
10-100 mVs-1
is shown in the Fig. 6c which indicates the process occurring is adsorption controlled. The relationship
between the anodic peak potential and scan rate is explained by plotting the anodic peak potentials vs. natural logarithm
of scan rate (Fig. 6d) by considering the liner regression equation given by
Epa (mV) = 0.01443lnυ +0.43687 R= 0.99754……………………………. (2).
The relationship between the anodic peak current and scan rate is explained by plot of the logarithm of anodic peak
current vs. logarithm of scan rate (Fig. 6e) by considering the following equation:
logIpa= 0.8266logυ -0.15702 R= 0.9873…………………………… (3)
The slope of 0.82 is close to the theoretically expected value of 1.0 for an adsorption controlled process [19] and as a
result the peak potential shifts towards positive side.
According to Laviron‟s theory [20] the slope is equal to RT/αnαF. As for a totally irreversible electrode reaction on the
basis of the above discussion, the nα was found to be 0.806, which indicated that one electron was involved in the
oxidation process of LTY at the poly (DICY) modified carbon paste electrode. Since the equal number of electrons and
protons took part in the oxidation of LTY, therefore one electron and one proton transfer were involved in the electrode
reaction process. The electrochemical reaction process for LTY at poly (DICY) modified carbon paste electrode can
therefore be summarized as in Scheme I.
Fig.6a: Cyclic voltammograms of 0.1 mM LTY at poly (DICY) modified carbon paste electrodewithdifferentscan rates (a) 10,
(b) 20, (c) 30, (d) 40, (e) 50, (f) 60, (g) 70, (h)80, (i) 90, (j) 100mVs-1
.

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0 20 40 60 80 100
5
10
15
20
25
30
35
40Ipa
()
 (mVs
-1
)
Fig.6b: Plot of anodic peak current vs. scan rates of LTY at poly (DICY) modified carbon paste electrode.
3 4 5 6 7 8 9 10 11
5
10
15
20
25
30
35
40
Ipa
()

1/2
(mVs
-1
)
Fig.6c: Plot of anodic peak current (Ipa) vs. square root of scan rates of LTY at poly (DICY) modified carbon paste electrode.
2.0 2.5 3.0 3.5 4.0 4.5 5.0
700
750
800
850
900
950
1000
Epa
(mV)
ln (mVs
-1
)
Fig.6d: Plot of anodic peak potential vs. natural logarithm of scan rates of LTY at poly (DICY) modified carbon paste
electrode.

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1.0 1.2 1.4 1.6 1.8 2.0
0.6
0.8
1.0
1.2
1.4
1.6
logIpa
()
log (mVs
-1
)
Fig.6e: Plot of logarithm of anodic peak current vs. logarithm of scan rates of LTY at poly (DICY) modified carbon paste
electrode.
Scheme.I: Probable Reaction Mechanism of L-Tyrosine.
3.7 Effect of L-Tyrosine (LTY) concentration and detection limit:
The effect of LTY concentration was studied by cyclic voltammetry in 0.1M phosphate buffer solution (PBS) of pH 6.5 at
the scan rate 50 mVs-1
. The oxidation peak current increases with increase in concentration of LTY. Fig. 7a and Fig. 7b
shows the linear relationship between the anodic peak current (Ipa) with LTY concentration in the range from 2×10-5
M to
1×10-3
M. The corresponding linear regression equation is
Ipa (µA) =26.5481 C (10-5
M) + 2.26913 (R = 0.9984)…………….. (4)
The limit of detection (LOD) and limit of quantification (LOQ) of LTY were found to be 0.638 µM and 2.128 µM
respectively. Related stastical data of calibration curves were obtained from five different calibration curves (n=5).
The LOD and LOQ were calculated from the peak current using the following equation:
LOD = 3S/M and LOD = 10S/M
Where S is standard deviation and M is the slope (sensitivity) of calibration plot.
200 400 600 800 1000 1200
Current(A)
j
a
28.7
Voltage (mV)
Fig.7a. Effect of variation of concentration of LTY (a) 2×10-5
M, (b) 4×10-5
M, (c) 6×10-5
M, (d) 8×10-5
M, (e) 1×10-4
M, (f) 2×10-4
M,(g) 4×10-4
M, (h) 6×10-4
M,(i) 8×10-4
M, (j) 1×10-3
Monanodic peak current at poly (DICY) modified carbon paste electrode; pH
6.5, scan rate 50 mVs-1
.

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0.0 0.2 0.4 0.6 0.8 1.0
0
5
10
15
20
25
30
Ipa
()
Concentration of LTY/10
-5
M
Fig.7b: Plot of anodic peak current vs. LTY concentration at poly (DICY) modified carbon paste electrode.
4. CONCLUSIONS
In the present study, the poly (Dicyclomine Hydrochloride) modified carbon paste electrode based on the
electropolymerisation has been prepared for the electrochemical investigation of LTY. Results showed that the oxidation
peak current of LTY was improved at poly (DICY) modified carbon paste electrode. The electrochemical response is
diffusion controlled and irreversible in nature for LTY. A linear concentration range was found to occur from 2×10-5
to
1×10-3
M by CV. The probable reaction mechanism involved in the oxidation of (LTY) is also proposed.
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Electrochemical Behavior of L-Tyrosine at Poly (Dicyclomine Hydrochloride) Film Modified Carbon Paste Electrode: A Cyclic Voltammetric Study

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